This invention relates generally to a rotary shaft assembly and to a method for the production thereof and, more particularly, to such an assembly suitable for use in an exhaust turbo supercharger.
Rotary shafts having both ceramic and metal portions are desirable in high temperature environments such as those experienced in turbo superchargers. However, difficult problems are presented by the requirement for creating between the ceramic and metal portions a bond which is both mechanically strong and fluid tight. One method for joining a metal portion to a ceramic shaft is disclosed in Japanese patent application No. 60892/1984. According to that disclosure, a number of axially extending grooves are provided in the outer peripheral surface of a ceramic shaft and axial poles of soft metal are externally fitted therein. By heating and deforming metal at the joint between the metal and ceramic portions a composite member having mechanical strength is obtained. However, a micro-sized clearance between the fitted portions fails to provide a tight fluid seal.
The object of the present invention, therefore, is to provide a composite metal and ceramic shaft which exhibits a high mechanical strength, provides a fluid tight seal, and is stable during large thermal cycles.